CLI: add nodes canvas snapshot + duration parsing

src/cli/nodes-canvas.test.ts

@@ -0,0 +1,20 @@
+import { describe, expect, it } from "vitest";
+
+import { parseCanvasSnapshotPayload } from "./nodes-canvas.js";
+
+describe("nodes canvas helpers", () => {
+  it("parses canvas.snapshot payload", () => {
+    expect(
+      parseCanvasSnapshotPayload({ format: "png", base64: "aGk=" }),
+    ).toEqual({
+      format: "png",
+      base64: "aGk=",
+    });
+  });
+
+  it("rejects invalid canvas.snapshot payload", () => {
+    expect(() => parseCanvasSnapshotPayload({ format: "png" })).toThrow(
+      /invalid canvas\.snapshot payload/i,
+    );
+  });
+});